Powerful and irresistible is the tendency to generate; in a great many cases the individual sacrifices himself consciously, or is unwittingly sacrificed by the laws of nature, provided that before death he transmit life to others. "Let the individual perish, if this preserve the species!" Such is the eternal cry of nature, which men and infusoria, oaks and mushrooms alike must obey. If the individual is protected and possesses preservative instincts and defensive organs, the species has a hundred bulwarks, a thousand manners of safeguard, more means of protection than are needed. In fact, living beings generate so profusely that one species alone would pervade the earth if the various circles of expansion, falling in with each other, did not struggle among themselves, like the circles caused on the smooth surface of a lake by a handful of sand thrown upon it by a child. Apart from the manner in which life is transmitted, there is an amount of life which passes away, there is a certain amount of fecundity, and this may seem, at first glance, most whimsical, while it is governed by the laws of preservation.
To be born and to die—fecundity and mortality—are so closely connected with each other that we can consider them as different aspects of the same phenomenon, as the action and reaction of life. When reproduction increases beyond measure, the dangers for the individuals generated increase at the same time, and destruction mows down the excessive number of those which are born. Now it is food that is no longer proportionate to the new-born; then parasites and enemies of the over-expanded species, which, increasing in turn, reëstablish the equilibrium. The destructive forces and the protective balance mutually, as happens with many other forces, simpler and better known.
The Malthusian problem, however, is much more intricate. If all species were equally prolific and had a life of equal length, the problem would, in fact, be reduced to a question of space and food; but, on the contrary, the duration of life and the various degrees of fecundity serve in turn to reëstablish the equilibrium by other ways. If the reproduction of mice were as slow as that of man, they would all be destroyed before another generation could be born; and even if they could live fifteen or sixteen years, not one of them, perhaps, would ever attain that age, surviving all dangers. And on the other hand, should oxen multiply in the same proportion as infusoria, the entire species would die of hunger in a week.
In order that an organic form be preserved, the individual must preserve itself and generate other individuals. Now these forces must vary inversely. If the individual, through its simple organization, is little fit to resist danger, it must countervail this weakness with reaction, generating intensely. If, on the contrary, high qualities give it a great capacity for self-protection, it should then diminish its fecundity proportionately. If danger is reckoned as a constant quantity, inasmuch as capacity for resistance should be equal in all species, and does consist of two factors (faculty to maintain individual life and power to multiply it), these factors cannot but vary in opposite directions. This most simple and sublime law, which Herbert Spencer read in the great book of nature, is one of those that rule with the most inflexible tyranny the elementary phenomena of reproduction, as well as the highest and most complex phenomena of human love.
In the Diatomaceæ the fecundity by scission is gigantic: Smith reckoned that a single gnat could create a thousand million individuals in one month. A young Gonium, capable of scission after twenty-four hours, can produce in a week 268,435,456 individuals equal to itself. In other cases, the process of multiplication is not scissiparous, but endogenous, as with the Volvox; but the reproduction is always extraordinary. If all the individuals generated should survive, a Paramecium would, by scission, produce in the course of a month 268,000,000 individuals. Another microscopic animal can produce 170,000,000,000 individuals in four days. The Gordius—the entozoön of an insect—lays 8,000,000 eggs in less than a day. An African termite lays 80,000 eggs in twenty-four hours, and Eschricht reckoned at 64,000,000 the number of eggs in the adult female of an Ascaris lumbricoides.
If, from the minute microscopic creatures exposed to every danger and which consume very little matter—if, from these living atoms of which you could gather as many in your hands as there are men on earth, you pass to the elephant, you have there a giant of flesh that requires thirty years of its life to become fecund, and then, after a long gestation, produces but one offspring. And above the elephant you find a giant of thought, Man, who requires the third part of his average life to reproduce himself, and after nine long months generates one child only; and, what is worse, he sees half of his offspring mowed down before they are able to bear flower and seed.
The methods of transmitting life are manifold, since nature in no other function has been so inexhaustibly rich with forms as in generation; but we, dealing here with the general physiology of love, will reduce all the various generative forms to these few:
Separation or Scission.—The individual dissevers into two parts, and each of these, made independent, reproduces the generator. This is the most simple form of genesis, in which the function of reproduction is not distinct from the other functions, but merges into them.
Endogenesis.—Within an individual many other individuals are formed; the parent opens, and, destroying its own individuality, dissolves in its offspring.
The individual by itself alone generates other individuals.—The parent generates through special organs and without dissolving in its offspring. The individuals generated and separated from the generator are eggs, seeds, perfect organisms; but in every case these are always elements evolved within the generator through special organs. The generative function is already marked and distinct in a laboratory which detaches and prepares some of the elements of the individual, so that they may reproduce it.
Monœcious Sexual Generation.—A step higher, the generative laboratory becomes complicated and divides into two parts, one of which brings forth the egg, the other the fecundating element. Each, for its own account, prepares the element destined for the reproduction of the individual; but if both do not come in contact, the new being is not generated. We have the sexes quite distinct, but enclosed within a single individual. Strange to observe, however, we behold an individual that generates an egg which cannot be fecundated by that individual's seed; or an individual that produces a seed which cannot be of any service to the egg. A duplex embrace of two hermaphrodites which interlace a quadruple love, and the appearance of winds, insects, or birds, as fecundatory paranymphs, resolves these problems of a most singular generation.
Diœcious Sexual Generation.—Finally, the generating organs, too, separate and fix themselves each upon a single individual, which is sterile in itself, produces but one of the generating elements, and, therefore, must combine with the other; and by such union they may produce the new creature: the sum of two individualities, the male and the female, the father and the mother. Man loves in twain; but although, like the other superior animals akin to him, he presents a diœcious sexual generation, yet in his inmost tissues he also possesses the endogenous genesis and the genesis by scission, and presents in this regard the remains also of the elementary forms of life enclosed within him.
In this rapid course through all the forms of generation we see delineated the same laws by which nature rules the other functions. Gradually new forces appear and new organs are brought forth to represent the subdivision of work. First, it is the whole individual that generates, then an organ of the individual, then again two organs in the same individual, and again two organs in separate individuals. In the many forms of genesis, the unity of the plan is more than ever manifest, and we, the highest of all living creatures, while, like the amœba, we have in our protoplasm and scattered all through the mass of our body the faculty to generate, recognize in man and woman the two distinct laboratories which prepare the seed and the human egg.